For the past seventeen years, courts in the Sixth Circuit required plaintiffs to prove that their disability was the “sole” reason for the adverse employment action taken against them. However, that changed when the Court handed down their en banc decision in Lewis v. Humboldt Acquisition Corporation, Inc. [pdf]. Relying upon the text of the ADA, the Court in Lewis held that because the ADA prohibited discrimination “because of” disability, the ADA prohibited discrimination that was the “but-for” cause of the employer’s adverse employment decision.
Michigan is in the 6th Circuit, so this decision will apply to ADA cases here.
This decision may stop defendants in ADA cases from trumping up work problems in order to make their firing for disability include some none disability-related issue-meaning that the disability wasn't the "sole" reason for the firing..
It basically says that, even if there are work related problems, if the the firing wouldn't have occurred "but for" the disability, then it's a real ADA complaint.